Algebraic Foundations
TL;DR
Algebra is like a puzzle where you use letters to represent unknown numbers. You'll learn how to follow rules to move these numbers around and solve for the unknowns. Mastering these basics makes harder math much easier to understand.
1. The Mental Model
Think of algebra as a balancing scale. Whatever you do to one side, you must do to the other to keep it balanced. Our goal is always to get the unknown ("x") by itself.
2. The Core Material
What's a Variable?
A variable is just a letter (like x, y, or a) that stands in for an unknown number. We use them because we don't know the number yet, or it could be any number in a set.
Expressions vs. Equations
- An expression is a combination of numbers, variables, and operations (like addition, subtraction, multiplication, division). It doesn't have an equals sign.
- Examples:
3x + 5, y - 7, 2ab
- An equation is like a full sentence in math; it states that two expressions are equal. It always has an equals sign
=.
- Examples:
3x + 5 = 11, y - 7 = 2, 2ab = 12
The whole point of an equation is usually to find the value of the variable that makes the statement true.
Basic Operations and Inverse Operations
To solve an equation, we use inverse operations to "undo" what's been done to the variable.
- Addition (+) and Subtraction (-) are inverse operations.
- If you have
x + 3 = 8, to get x alone, you subtract 3 from both sides: x + 3 - 3 = 8 - 3, so x = 5.
- If you have
x - 4 = 10, to get x alone, you add 4 to both sides: x - 4 + 4 = 10 + 4, so x = 14.
- Multiplication (× or juxtaposition) and Division (÷ or /) are inverse operations.
- If you have
2x = 10 (which means 2 * x), to get x alone, you divide both sides by 2: 2x / 2 = 10 / 2, so x = 5.
- If you have
x / 3 = 4, to get x alone, you multiply both sides by 3: (x / 3) * 3 = 4 * 3, so x = 12.
The Order of Operations (PEMDAS/BODMAS)
When you have multiple operations, you need a specific order to solve or simplify:
1. Parentheses (or Brackets)
2. Exponents (or Orders/Powers)
3. Multiplication and Division (from left to right)
4. Addition and Subtraction (from left to right)
This order is critical for evaluating expressions and simplifying parts of equations correctly.
3. Worked Example
Let's solve the equation: 3x + 7 = 19
- **Isolate the